Paraffinic slack wax as a dewaxing aid for lubricating oils

ABSTRACT

AN IMPROVED PROCESS FOR THE PRODUCTION OF BRIGHT STOCK OF IMPROVED POUR POINT AND HAZING CHARACTERISTICS WHICH PROCESS COMPRISES BLENDING A RESIDUAL LUBRICATING OIL STOCK WITH SLACK WAX AND THEN SUBJECTING THE BLEND TO SOLVENT DEWAXING.

United States Patent US. Cl. 208-27 8 Claims ABSTRACT OF THE DISCLOSURE An improved process for the production of bright stock of improved pour point and hazing characteristics which process comprises blending a residual lubricating oil stock with slack wax and then subjecting the blend to solvent dewaxing.

This application is a continuation-in-part of our copending application Ser. No. 553,727, filed May 31, 1966 now abandoned.

Our invention relates to an improved process for producing bright stocks from certain residual derived stocks.

It has previously been suggested in the art to prepare lubricating oils, including bright stocks, by subjecting crude lubricating oil stocks to a variety of treatments including deasphalting, solvent extraction, comparatively severe hydrogen treatment, sometimes called hydrotreating, solvent dewaxing, acid treatment, clay contacting and more recently, mild hydrogen treatment, sometimes called hydrofinishing. This last mentioned mild hydrofinishing operation in many instances is employed in lieu of acid treatment and clay contacting and is employed mainly in the treatment of lubricating oil base stoclw, as distinguished from crude lubricating oils, in order to remove odor and color forming materials which are considered to be objectionable in the final lubricating oil product. All of the above-mentioned operations contribute to the production of the final finished lubricating oil from the crude lubricating oil stock by removing undesirable constituents and/ or hydrocarbon types from either the crude lubricating oil stock or the intermediate lubricating oil base stock. Generally, the prior art does not suggest any preferred order in which these various operations are to be conducted other than that dictated by economic or engineering expediencies such as, for example, employing previously a treating technique which is effective to remove materials deleterious to subsequent treatment steps or which reduces the quantity of material to be treated in a subsequent step, the operation of which is more expensive.

One of the required characteristics or properties of a finished lubricating oil is that it be clear or bright and free from any cloud or haze even after storage at a low temperature for a period of time. In many instances this desirable characteristic or property of a lubricating oil can be obtained when employing any combination of one or more of the above-mentioned treating techniques. A

3,576,735 Patented Apr. 27, 1971 Another of the required characteristics or properties of a finished lubricating oil is that it have a low pour point. The desiredlevel of the pour point of a finished lubricating oil varies, depending upon the type of finished lubricating oil desired as a product and its intended employment. Usually, however, a pour point of +l0 F. or lower is required. In some instances the desired pour point may even be as low as 40 F. or even lower. In most instances, however, a finished lubricating oil having a pour point of about 5 F. to about +5 F. is satisfactory. The art has recognized for many years that the pour point of a lubricating oil is generally related to the quantity of wax present in the material and a variety of dewaxing techniques have been suggested to lower the wax content of lubricating oils and concomitantly lower the pour point thereof. Presently, the technique employed widely in the art is a solvent dewaxing operation. Even though present day solvent dewaxing techniques are generally considered to be somewhat of an improvement over techniques previously employed in the art, the solvent dewaxing treatments are still beset by the traditional problem in the dewaxing field, i.e. the wax cannot be removed from the lubricating oil without cooling the material being treated to an extremely low temperature, usually lower than the desired pour point of the finished product. Thus, the limiting factor in most solvent dewaxing operations is the refrigeration capacity of the unit and any technique which would permit obtaining the desired pour point of the treated material but permit employment of a dewaxing temperature even a few degrees above what might otherwise be required, results in a substantial improvement and enhancement of the process from an economic viewpoint.

In many instances this desirable characteristic of a low pour point in a lubricating oil can be obtained when employing a solvent dewaxing treatment in combination with any one or more of the treating techniques mentioned previously. A typical example of the prior art operation includes solvent dewaxing an intermediate lubricating oil base stock followed by acid and clay contacting of the dewaxed base stock. In more modern refinery operations this scheme would require solvent dewaxing of a lubricating oil base stock followed by hydrofinishing of the dewaxed material to yield the finished lubricating oil. While this sequence of operations may in some instances be entirely satisfactory to yield a lubricating oil having the desired pour point in an economical manner, it has been found that in many instances this sequence is not advantageous.

We have discovered that, when treating lubricating oil base stock derived from a residual material in order to produce bright stocks, the more conventional techniques of lubricating oil treatment are not satisfactory to produce a finished bright stock which is free of haze. Thus, for example, when employing the conventional technique of fractionating the entire crude lubricating oil into the various boiling range fractions required to produce light, medium and heavy distillate lubricating oils as Well as bright stocks and then subjecting these individual fractions to solvent extraction such as, for example, furfural extraction, under the particular difierent operating conditions which are optimum for each of the fractions and then dewaxing and hydrofinishing the fractions, the bright stock product obtained is usually quite hazy. We have found, however, that a haze-free bright stock product can be obtained in accordance with our invention if the lubricating oil base stock derived from a residual material, which is the source of the bright stock, is blended with paraffinic wax of the type present in distillate crude lubricating oils and distillate lubricating oil base stocks and then the blend is subjected to solvent dewaxing. The production of the 3 finished bright stock would, of course, also require a hydrofinishing treatment.

The particular materials which are to be treated in accordance with the process of our invention and which are the typical materials from which finished bright stocks are usually obtained can be described as having been derived from a residual material. Normally, a residual material or residuum can be defined as the higher boiling, diflicultly vaporizable components of petroleum hydrocarbons. These difiicultly vaporizable materials are usually of such a high boiling point that there is a tendency to effect some cracking prior to or along with distillation at atmospheric pressure. Generally, these materials will be found to boil above about 900 or 925 F. and include those materials which can only be distilled, without cracking, under a vacuum. It is lubricating oil base stocks derived from such residual materials that are contemplated for employment in our process. Generally, by the term lubricating oil base stock is meant a fraction or group of fractions usually produced at an intermediate point in the production of a lubricating oil which lacks but the final finishing operations, such as, for example, dewaxing, hydrofinishing, acid treatment or clay contacting, before being classed as a finished lubricating oil. Normally, such lubricating oil base stocks can be obtained from crude lubricating oil stocks, i.e. untreated materials boiling in the general lubricating oil range of 650 F.+, by atmospheric and vacuum distillation followed by various treatments, including solvent extraction, treatment in a Duo Sol process, comparatively severe hydrogen treatment, i.e. hydrotreatment, etc. or any combination of these treatments depending mainly on the type of crude lubricating oil being considered and the type of finished lubricating oil desired as product.

The particular lubricating oil base stock contemplated for treatment in accordance with our invention is, as mentioned above, a residual derived lubricating oil base stock and such material will usually have been subjected to a deasphalting treatment such as propane deasphalting. As distinguished from this particular lubricating oil base stock, which is the source of finished bright stock, the remaining lower boiling lubricating oil base stocks can be termed distillate lubricating oil base stocks and the portion of the crude lubricating oil from which they are obtained can similarly be termed a distillate crude lubricating oil. At times, however, there may be a certain overlap in the boiling ranges of what are termed distillates as distinguished from the residual derived lubricating oils or lubricating oil base stocks. Thus, while the residual derived materials will generally have an initial boiling point of 900 or 925 F. or above they will usually be found to have a 5 percent boiling point closer to 950 F. and a percent boiling point above 950 F. On the other hand, however, while certain of the heavier distillate lubricating oil base stocks may have 90 percent boiling points or end boiling points as high as about 1000 F. they will usually be found to have 10 percent boiling points substantially below 900 F. but with initial boiling points and at least 5 percent boiling points of 650 F. or higher.

The residual derived lubricating oil base stocks treated in accordance with our invention can also have a comparatively high sulfur content, such as, for example, about 0.75 percent by weight or greater. In many instances it will be found that these stocks contain at least about 1.0 percent by weight sulfur.

The paraffinic wax which is blended with the residual derived lubricating oil base stock in accordance with our invention is of the type normally present in distillate crude lubricating oils or distillate lubricating oil base stocks and thus comprises waxes boiling above about 650 F. and preferably above about 700 F. These waxes are wellknown in the field of lubricating oil production and, for example, when this paraffinic wax has been removed from a distillate lubricating oil base stock by means of solvent dewaxing the Wax recovered is generally termed a slack wax. It is within the scope of our invention to add the paraflinic wax to the residual derived lubricating oil base stock either in the form of the wax itself, such as, for example, a deoiled slack wax or a slack wax, or to introduce such paraffinic wax into the blend simply by adding a quantity of a distillate lubricating oil base stock containing such paraflinic wax to the residual derived lubricating oil base stock. We have found that it is advantageous to select, as the source of parafiinic wax, a distillate lubricating oil base stock boiling in a range substantially below that in which the residual derived lubricating oil base stock boils. The reason for this is that it is theorized that when employing a distillate lubricating oil base stock of a higher boiling range, the wax contained therein or obtained therefrom is composed of a greater proportion of microcrystalline wax whereas the extremely light lubricating oil base stocks contain substantially no microcrystalline wax. Thus, for example, we prefer to employ as the source of the paraffinic wax a distillate lubricating oil base stock having a percent boiling point of about F. lower than the 5 percent boiling point of the residual derived lubricating oil base stock and preferably about 100 F. lower than the initial boiling point of the residual derived stock.

When practicing our invention and employing the technique of adding the slack wax alone to the residual derived lubricating oil base stock, it is generally satisfactory to add to the base stock a quantity of slack wax equal to about 5 to about 50 percent by volume of the base stock. Preferably, however, the amount of the parafiinic wax added will be equal to about 10 to about 35 percent by volume of the residual derived base stock. When it is desired to blend paraffinic wax containing distillate lubricating oil base stocks with the residual derived lubricating oil base stock we have found that it is satisfactory to employ a quantity of distillate base stock equal to at least about 30 percent by volume of the residual derived stock. Generally, however, we prefer to employ at least about a 5050 blend of distillate base stock and residual derived base stock.

In the solvent dewaxing treatment of our invention we have found that any of the well-known solvents employed in the art to effect dewaxing are quite satisfactory. Generally, we prefer to employ methylethylketone and toluene in about a 5050 mixture as the solvent. The particular temperature employed in the solvent dewaxing treatment in accordance with our invention is usually about 5 F. or more above that required when not employing our processing sequence in order to provide a product iraving the desired pour point, usually about +10 F. or

ower.

In the hydrofinishing operation of our process the operating conditions employed can include a temperature from about 400 to about 850 F. and preferably from about 600 to about 750 F., a pressure in the range from about 800 to about 3000 p.s.i.g. and preferably from about 1000 to about 2000 p.s.i.g., a liquid hourly space velocity in the range from about 0.1 to about 10.0 and preferably from about 1.0 to about 4.0 volumes of lubricating oil base stock per volume of catalyst per hour and a hydrogen circulation rate in the range from about 1000 to about 20,000 s.c.f./b. and preferably from about 2000 to about 7000 s.c.f./ b. The catalyst employed in the hydrofinishing operation in accordance with our invention can be any of the hydrogenating catalysts well-known in the art, such as, for example, Group VI and Group VIII metals, their oxides and sulfides, or mixtures thereof, either alone or supported on a suitable carrier. Examples of catalysts which we have found to be advantageous for use in our invention are combinations of nickel, cobalt and molybdenum on an alumina support, such as, for example, a catalyst of the type described in US. Pat. 2,880,171, and a combination of nickel and tungsten on alumina. Catalysts such as these can also contain a small quantity of silica, such as, for example, less than about percent by weight or even lower.

In order to illustrate our invention in greater detail, reference is made to the following examples.

EXAMPLE I Another bottoms fraction obtained from the same Kuwait crude mentioned above was subjected to propane deasphalting and furfural extraction under substantially the same conditions described above so as to provide a deasphalted, solvent extracted bottoms fraction substan- 5 tially identical to that shown in Table II. This bottoms In this example a Crude lubricatlng 011 Stock l e fraction was then separately subjected to dewaxing, i.e. from a reduced Kuwait crude having components boiling in the absence of any light, medium or heavy distillate, up to about 1100 F. was subjected to vacuum distillaafter which it was subjected to hydrofinishing under the tion so as to separate the crude lubricating oil into light, same conditions set forth previously. The following Table medium and heavy distillate fractions as well as a bottoms III shows comparative inspection data on the two finished fraction. The inspections for these various fractions are bright stocks obtained in accordance with the two techshown in Table I below. niques described above, i.e. dewaxing the bright stock TABLE I Light Medium Heavy Botdistillate distillate distillate toms Inspections:

Gravity, API 25.2 20.0 17.7 6.5 Viscosity, SUS at- 10 114.6 475 1,700 40.0 57.5 94.0 8,233 Sulfur, percent by weight- 2: 10 jl 05 5.3 Carbon residue, grams, percent by wt 0. 11 0. 50 1.07 12. 8 Distillation, ASTM D1160, F. at-

The bottoms fraction was then subjected to propane dealone and dewaxing the bright stock and distillate fracasphalting at a pressure of 500' p.s.i.g., a temperature at tions together. the tower top of 150 F. and at the tower bottom of TABLE m 120' F. The inlet temperature of the oil was 127 F. The ratio of propan e to oil on a volume to volume basis emgg g g ggg ployed in predllutlon was 0.5 and in the strlpplng was alone distillats 7.5, yielding 31.8 percent by volume of deasphalted oil Dpwaxingtempemtmeg F having an API gravlty of 20.5, a viscous SUS at 210 F. Fmi sj ed brighg Stocgr: a 7 of 19 6 and containing 2.70 percent by weight sulfur. fifiigfig fi ffj 31 The light and medium dlstillates were then blended topp z g cez 1 2 gether and subjected to furfural extraction while the i sf f g g- 53 ;g 'g m g heavy distillate and deasphalted bottoms fractions Were I; hth each subjected to furfural extraction separately. The par- 2 5, ticular operating conditions employed in each of the thug; solgient extlgiclillollg together with blnspectlon data From the data in Table III above it will readily be of e m Dates 0 tame 18 S Own m Ta 16 H belowseen that when operating in accordance with the process TABLE II of our invention wherein the paraffinic wax containing distillate fractions are blended with the residual derived g'g gg' Heavy bright stock source the finished bright stock obtained is distillate distillate Bottoms haze-free while the finished bright stock product from Furfuml extraction, the more conventional operation wherein the bright stock Conditions: is dewaxed separately is subject to a hazing problem. It 2g gtft$ bg 5 2: 8 will also be noticed that while both bright stocks were Tower bottom teinn, 150 170 210 dewaxed at the same temperature of 15 F. the finished ggai? g jg 17 398 5% bright stock obtained in accordance with our invention Inspectior 1s: had a pour point of 10 F. as opposed to the pour point g'g of 0 F. of the more conventionally obtained finished 100 F 107.1 500 bright stock. Thus, in addition to eliminating the hazing Viscosity index Z1? problem in bright stocks the process of our invention also Sulfur, percent by wt 1. 9 .53 .57 permits a significant saving in refrigeration capacity required in the dewaxing unit.

The solvent extracted, paraffin wax containing light In p f g t0 ln a finished bright stock by the medium and heavy distillate fractions were then blended more conventlona} mqueof Separately dewaxing, We with the bottoms fraction and subjected to solvent dehave: found that It has been onecessal'y to Fmploy Waxing employing a 55-45 blend of methylethylketone waxmg temperature of to provolde a fimshed and toluene at a solvent to oil ratio, on a volume to bngh t havmg 3 Pour Pomt of [Elms volume basis, of 45 and at a temperature of stantlatmg the fact that the process of our lnventlon con- The amount of paraffin wax in the distillate fraction was slstenfly t a Savings 1n refrigeration capacity of equivalent to about 35 percent by volume of the bottoms about 10 m obtammg fimshed bnght stockfraction. 'Ihis dewaxed blend was then subjected to hy- EXAMPLE H drofinlshlng at a temperature, measured at bed outlet, of about 700 F, a pressure of 1650 psig and a liquid In this example a crude lubricating oil stock obtained hourly space velocity of 3.0. The hydrofinished lubricatfrom a reduced Kuwait crude having components boiling ing oil was then fractionated to obtain finished light, meup to about 1100" F. and above was subjected to vacuum dium and heavy distillate lubricating oils and a finished distillation so as to separate the crude lubricating oil into bright stock. light, medium and heavy distillate fractions as well as a bottoms fraction. The inspection data for this bottoms fraction were identical to those shown for the bottoms fraction in Table I of Example I. This bottoms fraction was then subjected to propane deasphalting under the same conditions set forth in Example I so as to provide a deasphalted oil having the same API gravity, viscosity and sulfur content as is also set forth in Example I. This deasphalted bottoms fraction was then subjected to furfural extraction, again employing the operating conditions employed for the bottoms fraction in Example I and set forth in Table II thereof. The results of this solvent extraction were substantially the same as those obained in Example 1 providing a yield of 62 percent by volume of raffinate having an API gravity of 25.4, a viscosity SUS at 210 F. of 158 and a sulfur content of 1,31 percent by weight. This deasphalted, solvent extracted bottoms fraction was then separately subjected to solvent dewaxing employing a 55-45 blend of methylethylketone and toluene at a solvent to oil ratio. on a. volume to volume basis, of 5.4 and at a filtration temperature of -16 F. After having been dewaxed, the bottoms fraction was then hydrofinished at a temperature, measured at bed outlet, of about 675 F., a pres sure of 1755 p.s.i.g. and a liquid hourly space velocity of 1.7. The effluent from the hydrofinishing operation was then pased to a stripper from whence was obtained a bottoms stream in a yield of about 96 percent by volume based on charge to the hydrofinisher and a small side stream in a yield of about 6 percent by volume based on the charge to the hydrofinisher. The finished bright stock of the bottoms stream had a viscosity index of 98 and a pour point of F. while the finished side stream had a viscosity index of 95 and a pour point of +5 F. After 48 hours at 40 F. samples of the finished bright stock from the bottoms stream showed a light haze while samples from the side stream showed heavy floc.

In another operation in which the distillate fractions are also dewaxed separately from the deasphalted and solvent extracted bottoms fraction, a portion of the slack wax obtained from dewaxing the distillate fractions is blended with the bottoms fraction in an amount equivalent to about 15 percent by volume of the bottoms fraction prior to subjecting it to dewaxing. The blend of slack wax and bottoms fraction is then dewaxed under substantially the same conditions described above regrading the dewaxing of bottoms fractions, after which the dewaxed oil is subject to hydrofinishing, again under substantially the same conditions described previously in this example, to provide a finished bright stock. This particular finished bright stock shows no hazing tendencies after storage at 40 F. for a period of 48 hours.

\EXAMPLE III In this example a crude lubricating oil obtained from a comparatively low sulfur content Mid-Continent crude oil having components boiling up to about 1100 F. and above is subjected to vacuum distillation to provide light, medium and heavy distillate fractions as well as a bottoms fraction boiling generally above about 900 F. with a percent point of about 1000 F. The bottoms fraction is solvent deasphalted and then each of the crude lubricating oil fractions, i.e. the light, medium and heavy distillate fractions and the deasphalted bottoms fraction, is separately subjected to solvent extraction with a solvent selective for aromatics. Each of the intermediae lubricating oil base stocks obtained as the raffinate from the solvent extraction of the distillate fractions is then separately subjected to solvent dewaxing whereby slack wax is removed and the dewaxed distillate fractions are separately hydrofinished to yield finished distillate lubricating oils. The intermediate bright stock lubricating oil base stock obtained by deasphalting and solvent extracting the bottoms fraction and containing about 0.4 percent by weight sulfur is divided into two portions. One of these portions is then subjected to solvent dewaxing and the dewaxed material is then hydrofinished to produce a finished bright stock. The other portion of the lubricating oil base stock derived from the bottoms fraction is blended with a portion of deoiled slack wax obtained from the distillate fractions employing a quantity of deoiled slack wax equal to about 25 percent by volume of the lubricating oil base stock. This blend is then subjected to dewaxing followed by hydrofinishing of the dewaxed material to provide a second finished bright stock. After storage at 40 for a period of 48 hours the finished bright stock obtained from the first fraction, which was dewaxed in the absence of additional deoiled slack wax, was found to have a light haze whereas the finished bright stock obtained from the second fraction, which was dewaxed in the presence of additional deoiled slack wax, showed no haze.

EXAMPLE IV In this example a light distillate lubricating oil stock boiling in the range from above about 650 F. to about 850 F. was subjected to a conventional dewaxing treatment. The dewaxed light distillate lubricating oil stock and the slack wax obtained from the dewaxing were then recovered and subjected to a boiling range determination. Inspection data for both the undewaxed and the dewaxed light distillate lubricating oil as well as the slack wax' are set forth below in Table IV From the above data it will be seen that the slack wax obtained from a distillate lubricating oil stock is comprised of waxes of substantially the same boiling range as the lubricating oil from which obtained.

EXAMPLE V In this example a residual derived lubricating oil base stock containing at least 0.75 percent by weight sulfur is first subjected to hydrofinishing after which the hydrofinished stock is blended with about 25 percent by volume based on the hydrofinished stock of a slack wax obtained from a distillate lubricating oil stock boiling above 650 F. The blend of hydrofinished stock and slack wax is then subjected to dewaxing to produce a finished lubricating oil having greatly enhanced hazing characteristics and capable of being stored at 10 F for 48 hours without showing any tendencies to form fioc.

We claim:

1. An improved process for producing a bright stock from a lubricating oil base stock derived from a residual material boiling above about 900 F. which process comprises blending the residual derived lubricating oil base stock with from about 5% to about 50% by volume of said base stock of a slack wax obtained by solvent dewaxing a material boiling above about 650 F. and selected from the group consisting of distillate crude lubricating oils and distillate lubricating oil base stocks and then subjecting the blend to solvent dewaxing.

2. The process of claim 1 wherein the slack wax is deoiled slack wax obtained by solvent dewaxing a distil late lubricating oil base stock to yield slack wax and then deoiling the slack wax.

3. The process of claim 1 which further includes subjecting the dewaxed blend to hydrofinishing.

4. The process of claim 3 which further includes fractionating the dewaxed and hydrofinished blend so as to separate the finished bright stock from lighter components.

5. The process of claim 1 wherein the residual derived lubricating oil base stock contains at least about 0.75 percent by weight sulfur.

6. The process of claim 1 wherein the residual derived lubricating oil base stock has a 10 percent boiling point above about 950 F.

7. The process of claim 2 wherein the distillate lubricating oils and distillate lubricating oil base stock boil in a range at least about 100 F. below the boiling range of the residual derived lubricating oil base stock.

8. An improved process for,producing a bright stock from a lubricating oil base stock containing at least about 0.75% by weight sulfur and derived from a residual material boiling above about 900 R, which process comprises subjecting the residual derived lubricating oil base stock to hydrofinishing and thereafter blending the hydrofinished lubricating oil base stock with from about 5% to about 50% by volume of said hydrofinished base stock of a slack wax obtained by solvent dewaxing a material boiling above about 650 F. and selected from the group 10 consisting of distillate crude lubricating oils and distillate lubricating oil base stocks and then subjecting the blend to solvent dewaxing.

References Cited DANIEL E. WYMAN, Primary Examiner P. E. KONOPKA, Assistant Examiner US. Cl. X.R. 

